Which SMTP response code indicates that the requested action has been completed successfully?

The response code that indicates the requested action has been completed successfully is 250. This code is used by an SMTP server to confirm that a command was successfully processed. It's often seen as a response after actions such as a successful mail transfer or completion of the MAIL, RCPT, or DATA commands.

For instance, when a message is accepted for delivery, the 250 response is sent back to the client to indicate that the action completed without any errors. This helps establish successful communication between the client and server, confirming that the intended operation was performed as expected.

Understanding this code is essential for troubleshooting and managing email communications, as it directly signifies successful operations within the SMTP protocol.